Cyclic tearing and crack growth in circumferentially cracked straight pipes

Earthquake load, which is cyclic in nature and of short duration, is the main design basis accident load for designing the primary heat transport (PHT) piping components of Nuclear Power Plants. Adequate protection of piping components from the effects of earthquake requires detailed knowledge of strength and deformation characteristics of the components and assemblies making up the piping system. Fracture behaviour of 23 pipes was studied by conducting cyclic tests under four‐point bending. Fifteen pipes were of carbon steel (SA333 Grade 6) of 219 mm, 324 mm and 406 mm ODs and eight pipes were of stainless steel (AISI Type 304LN) of 168 mm OD with through‐wall circumferential crack. Six pipes were tested under displacement control and the rest under load control. The effect of various parameters such as location and size of initial crack in base metal and weld metal, cyclic load range and displacement increment on crack growth and number of cycles for failure was investigated. The investigations showed significant reduction in the fracture resistance under cyclic loading conditions. Crack growth equations have been proposed for carbon steel pipes with and without weld under cyclic tearing.